Electroacoustic device



Oct. 17, 1944. J. s. P. RoBERToN y 2,360,796

t ELECTRO-ACOUSTIC DEVICE I .Filed May 12,1942 2 sheets-shewA 1 wvl/50Min@ ay" l Patented Oct. 1 7, 944:

- James SamueVPatersonRobertomfLondon, Engi v v land,A assigner to International Standard Elecf tric Corporation, New York, N. I.

' vpp licaton May 12, 1942, SerialNo. 442,655 l Great Britain'November 29, 1940 f claims-tcl. 17in-114) This invention relates' to telephone receivers Vand transmitters,l and visapplicable to transmitters. jandI receivers' for A batteryless or @sounds powered telephones,`as well as to ordinary'telephone recei'versjused .on handsets andheadsets and as watch receivers. The units could be made in capsule form 'or' as `insets in whichthe parts are clamped together by the earcap.

linesfof magnetic flux will pass straight through thediaphragx'n, traversingit in a direction sup- Amongthe, featuresv of the invention is the* use cfa balancedfarinature principle, in which the armature is a. magneti c diaphrag m. This has the normal advantagesrof a balanced 'armature' stantially normal to its plane. Windings I6 and f 1 1 areassembled 'in the annular recesses of the v*magnetsand sealed'in with a suitable sealing f compound. The windings are connected together at'jld and insulated leads I9 and 2uconnect reyspectiyely to terminal 2| and case 22. The connection' and sense of the two windings is such that at any `instant when current 1s tiowing through them the Yradial magnetic uxes produced in the diaphragm I3 are additive, in other system. viz. high efllcienc'y due to polarising flux notpassing through the armature, and`no dis' tortion. ydue to harmonics.

In 4additionl it. has further 'aavantage's due tothe constructionadopted, viz., alight moving sys tem owing to cmbination'of armature anc l ,dia

. Phragm the` magnetic armature. can be made very fthin `beca1 ise.it does not carry polarising 1 '.ilux). the.ma`gnetfaces are ground 'in' the same plane andthe working gaps can be made very small` and, 8 .oc`uratel by using spacing washers of controlled thickness, and' a sealed-in' capsule construction can ,readily be applied to the desig'h,

Words the current at any instant will create poles of like polarity in juxtaposition on opposite 15 sides of the diaphragm. Thus, considering both `the steady 'flux and the ux due to speech (the term speech being of course a quite vgeneral one "and not limiting the use'of the instrument to the conveyance of human articulation), it may be saidthat substantially if not wholly, the fluxes traverse the diaphragm' in directions which are,

'for the steady flux, normal to its plane and for .with the advantage lof keeping magnetic par` ticles anddirt from the small airgaps of the balanced armature system.

" In order that the 'invention may be clearly understood, a description will given or `certain this purpose to the accompanying: drawings.

In those drawingss' Figs. l and` 2 are central sectionsfat right- A angles to one another'through a first embodi'f ment;

Figs. 3 and 4 are similar sections through a second embodiment:

Figs. 5 and 1'ai'esiniilar sectins .thoughma'i' ,f f' v 4a. Fig. 7 is a central section through a niodiflcathird; and

tion of the rst embodiment. Referring to Figs."1 an d 2, each of 't nets Il and I2 4is annular in shape.' with a chanT are magnetised with opposite polarity and are arranged face to face clamping between them' a, magnetic (i. e. ,.magnetisable) vdiaphragm I3 The" spaced by magnetic washers M and |5. inner poles of the two magnets are thus arranged in juxtaposition on opposite sides of the 'diaphragm; and as they are o1' oppositepolarity the e magi 3.0 V of its embodiments, referencebeing made f or the ilux due to speech parallel to itsplene. It

-will be 'clear that according to the direction of the 'current and hence of the radial fluxes produced, the'diaphra'gm will be deected towards either magnet' Il or magnet l2. y Y

The magnets, coils and diaphragm are assembled inside a casing 23A preferablyof moulded insulating material. The terminal`2| is of circular shape with a projecting tag and is located centrally in a recess in the casing 23. The tag is formed at right angles and enters a, longitudinal groove-ln the cylindrical wall of casing 23. A

central h'ole in terminal 2l iscovered with acousf'tic resistance material 24 such as sill-r, and is a continuation of a similar hole in case 23. An

" insulating washer 25 is of such a size that it just overlaps terminal l2l andserves to insulate it from the voutermetal case 22. The latter is preferably of thin sheet non-'magnetic metal, and has an aperture rather larger than that in the 'jwasherzaf-The; fiat -e'nd surfaces of terminn 2l'and cas 2 2 then serve as conducting surfaces nel section, havingl an' inner ring forming oneff45 pole and an outer ring forming the other pole of the maget. The polar facesare preferably ground in the saine plane. The twomagnets Il and l2 vto vwhich external connection mayl be made by means of contact springs; they may be plated "with highlyfconducting metal such as silver.

After assembly of thel magnet System in casing 23, and the Alatter in case 2 2, a-membra'ne 26 preierabiyof oiled'sill; or'similar material is added.- Thisls held in position by a metal plate 21 hav ing'a central aperture for egress of sound. The

" case'22 is then formedover the washer 21 by such means as spinning or pressing, completing the assembly.

The air chamber between the diaphragm I3, magnet I2 and casing 23, and the silk covered hole in casing 23 and terminal 2I, form the elements of an acoustic network which is designed to give improvement of the frequency characteristics of the receiver as disclosed in British Patent No. 481,351, corresponding to U. S. Patent No. 2,220,942.

Similarly, the air chamber between the diaphragm I3, magnet II, and plate 21, `together vwith the hole or holes in plate 21, and the hole or holes in the earcap associated with the receiver, form elements of another acoustic network which is designed to give a resonance within the frequency band 250G-3300 as disclosed in British Patent No. 481,740. The filling or sealing compound used to hold the coils I6 and I1 in position may be moulded to have a conical form as described in the latter patent. To prevent undue air damping the inner pole rings of magnets II and I2 may have one or more radial phragm I3 clamped between the casings, so that unlike poles of the two magnets are in juxta- 'position to one another on opposite sides of the diaphragm. The spacing washers I4 and I5, which preferably are of thin non-magnetic material and may he either metallic or non-metallic, are placed between each side of the diaphragm and the seats on the mouldings to space the magnets from the diaphragm by an amount equal to the washer thickness. Four windings 33, 34, 35 and 35, are assembled round the limbs of the magnets and sealed in by suitable compound to the recesses provided in the moulded casings 3| and 32. The four windings are connected in series and the insulated leads I9 and 20 are connected respectively to terminal 2l and case 22; grooves and recesses are provided in the mouldings for vpassage of the leads. The connection and sense of the four windings is such that at any instant when current is flowing in single energising coil 52 is used, and the ends are connected to terminal 2l and case 22 as before.

The coil is assembled on a core 53 of magnetic material which is fixed by screws 54 to pole pieces of magnetic material 55 and 56. The latter are moulded into the moulding 32 and project through so that their end faces lie close to the diaphragm surface.

A third moulding 51 encloses the coil and is recessed on its outside for terminal 2|.

The shallow chamber formed between the diaphragm and moulding 32, the hole in magnet I2 covered by a silk disc 58, and the air chamber enclosed between mouldings 32 and 51, together form an acoustic network which is designed in accordance with the principles disclosed in British Patent No. 481,351 to obtain a uniform response characteristic throughout a wide frebe of high permeability magnetic material such vto them the magnetic fluxes which they produce in the diaphragm traverse the diaphragm in a direction parallel with its plane, passing from one pole of a magnet to the opposite pole in the same sense so as to be additive. It will be clear that according to the direction of the current and hence of the magnetic flux produced, the diaphragm will be deected towards one or other of the two magnets lIol I2.

Figs. 5 and 6 show a third form of the'ixrvention. Two channel-section magnets II and I2 which preferably extend lengthwise to nearly the full width of the diaphragm I3, are magnetised with opposite polarity at each side of the channel. The magnets are moulded into two moulded casings 3| and 32 and the diaphragm is spaced byV washers I4 and I5 in the manner already described'for the designs of Figs. 1 to 4. The central part of diaphragm I3 which faces the central area of magnets II and I2, is made of non-magnetic material 5I attached by suitable adhesive to the diaphragm. This detail extends the full length of magnets II and I2 as seen in Fig. 6. A u

as an alloy comprising 78% nickel. 22% iron, or 45% nickel and 55% iron, so that magnetic screening of straymagnetism from the receiver magnets is thereby afforded to other apparatus with which the device is used. This is particularly necessary, for instance, where receivers and transmitters are used in aircraft near to a magnetic compass.

Any of the designs described may be arranged so as to have the driving force applied at the node of the rst nodal circle of vibration of the diaphragm. In the design of Figs. 1 and 2, this would correspond to placing the mean circle of the inner pole ring of the magnet at 37.9% of the clamping diameter. Designs Figs. 3 to 6 would have the poles so placed that they line on the nodal circle and are approximately bisected by it.

Fig. 7 is added as an alternative to the design shown in Figs.'1 and 2. In Fig. 7 there are two annular magnets II and I2, together with two yokes 1I and 12, of magnetically soft material, having projecting central portions. the magnetic circuit as before completing Aits path radially through the armature I3.

What is claimed is:

1. An electro-acoustic reproducer including a magnetic diaphragm, channel shaped magnets positioned on each side and near the central portion thereof, having unlike poles opposite one another, and a speech coil system including an open ended elongated coil having a core and two pole pieces both positioned on one side of said diaphragm, and near the periphery thereof.

2. An electro-acoustic transducer of the type comprising a permanent magnet system, a diaphragm of magnetic material and a speech coil system, in which said diaphragm of magnetic material is so arranged in relation to said magnet system that it is traversed by the steady magnetic flux due thereto and is so arranged in relation to said speech coil system that it is traversed by the alternating magnetic ux due thereto, and in which said speech coil system is spaced from said permanent magnet system and diaphragm and is formed in an elongated shape having a core with pole pieces at opposite ends thereof, said pole pieces being. positioned adjacent said diaphragm and in such a manner that the magnetic ux due to said speech coil system traverses said diaphragm in the plane thereof, the relative positions of said permanent magnet system and said pole pieces with reference to net system that it is traversed by the steady 10 magnetic ux due thereto, and is so arranged in relation to said speech coil system that it is traversed by the alternating magnetic flux due thereto, said magnet system comprising two similar channel-section magnets, withtheir poles 15 at each side oi the channel, arranged with their opposite poles in juxtaposition on opposite sides 'of said diaphragm, said diaphragm having two magnetic parts separated by a diametral nonmagnetic part lying within the channels. and said speech coil system being spaced from said magnet system and diaphragm and formed in an elongated shape having a core with separate pole pieces at opposite ends thereof, each pole piece being positioned adjacent one of said mag'- netic parts of said diaphragm, whereby the magnetic lilux due to said speech coil system traverses said diaphragm in the piane thereof.

.mr/ms SAMUELY PATERsoN ROBERTON. 

